Acinetobacter baumannii is a Gram-negative, aerobic, nonfermenting bacterium recognized over the last decades as an emergining pathogen with very limited treatment options.
A. baumannii is considered to be a serious threat by the US Centers for Disease Control and Prevention and belongs to the so called ‘ESKAPE’ pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species & E. coli) that currently cause the majority of nosocomial infections and effectively “escape” the activity of antimicrobial agents.
A. baumannii is most often encountered in intensive care units and surgical wards, where extensive antibiotic use has enabled selection for resistance against all known antimicrobials and where it causes infections that include bacteremia, pneumonia, meningitis, urinary tract infection, and wound infection.
A. baumannii has an exceptional ability to upregulate and acquire resistance determinats and shows an environmental persistance that allows its survival and spread in the nosocomial setting, making this organism a frequent cause of outbreaks of infection and an endemic, health care-associated pathogen.
Due to increasing antibiotic resistance to most if not all available therapeutic options, Muti-Drug Resistant (MDR) A. baumannii infections, especially those caused by Carbapenem resistant A. baumannii, are extremely difficult or even impossible to treat with high mortality rate as well as increased morbidity and length of stay in intensive care unit.
Acinetobacter baumannii has been defined and still remains “a prime example of a mismatch between unmet medical needs and the current antimicrobial research and development pipeline” according to the Antimicrobial Availability Task Force (AATF) of the Infectious Diseases Society of America (IDSA). Thus, there is a high demand and need to identify compounds suitable for the treatment of diseases and infections caused by Acinetobacter baumannii. 
The present invention provides a novel chemotype (peptide macrocycles) that exhibits activity against drug-susceptible as well as drug-resistant strains of Acinetobacter baumannii. The molecules have been routinely tested against drug susceptible A. baumannii strains (ATCC19606 and ATCC 17978) and in addition over a panel of ten clinical isolates. Some representative molecules were selected for in vivo profiling. Both, the pharmacokinetic profile as well as the efficacy in a mouse septicemia model are indicative of a great potential for further development of the compound class.